Compositions for fluid transmission of power



Patented May 30,. 1939 UNITED STATES COMPOSITIONS FOR FLUID TRANSMISSIONOF POWER William Percival Smith, London, England No Drawing.

Application July 17, 1937, Serial No. 154,320. In Great Britain November18,

Claims.

This invention relates to compositions for fluid transmission of power,and the present application is filed as a continuation in part of myapplication for patent for improvements in or relat- 5 ing toCompositions for fluid transmission of power, Serial No. 743,011, filedSeptember 6, 1934.

Recent developments in the design of fluid pressure brakes inautomobiles have imposed more exacting conditions on fluid transmissioncom- ]0 positions in that such compositions are required to stand a muchhigher temperature than formerly and many compositions hitherto foundsuitable for this purpose have been found to vaporize at thetemperatures to which they are. now subjected, and it is one object ofthis invention to provide a liquid with an unusually high vaporizingpoint while retaining the properties which are well known to beessential for these liquids, such as low freezing point, constantviscosity over a large range of temperature and absence of action on themetal and rubber parts of the mechanism.

Castor oil, on account of its constant viscosity over a wide range oftemperatures has been used largely as a fluid for transmission of power,in

particular in fluid braking systems, and in order to overcome as far aspossible the alleged detrimental efiect of castor oil upon the rubberparts of the mechanism, alcohol has been added to the castor oil.

It has also been proposed to incorporate with castor oil certain estersof the type of di-butylphthalate with a view to obtaining a solution Iwhich is more stable and gives a more constant viscosity of the castoroil with change of temperature.

I have now found that the acetic acid esters of polyhydric alcohols arepre-eminently suitable.

as constituents for brake fluids and liquids for other fluidtransmission systems because the resultant liquid will remain in theliquid state down to a very low temperature and will withstand very hightemperatures without appreciable vaporisation. In particular I havefound triacetin to be pre-eminently suitable as a constituent for brakefluids because it remains liquid down to a temperature of C. and has aboiling point of 258 C. I have found, however, that other polyhydricalcohol esters of acetic acid give highly satisfactory results whenincorporated 50 with castor oil as brake fluids, but generally speakingthe esters of polyhydric alcohols containing more than three hydroxylgroups are of no importance for the purpose of this invention.

One difliculty, however, has been to make a 2 compatible solution of thepolyhydric alcohol ester with the castor oil because triacetin and someof the other acetic acid esters of polyhydric alcohols are not misciblein the proportions which give the best results for the purpose of thepresent invention, and it was therefore necessary in such 5 cases tofind a suitable solubilizing agent which would not to any appreciableextent adversely affect the desirable properties attained by theassociation of the acetic acid ester with the castor oil.

I have now found that the glycol ethers generally as a class aresuitable solubilising agents, and more particularly the butyl ethers ofboth ethylene glycol and di-ethylene glycol are specially goodsolubilisers. The ethyl ether of. ethylene glycol is also suitable butthe ethyl ether of di-ethylene glycol is not itself sufficientlycompatible with castor oil to be used with proportions of castor oilgreater than about 10% unless some butyl ether is also employed with it.

Certain of the polyhydric alcohol acetic acid esters are compatible withcastor oil in considerable proportions without the aidof a solubilisingagent, while only a very small proportion of triacetin can be broughtinto compatibility with castor oil without the aid of a solubilisingagent, but minute quantities can, however, be brought into compatibilitytherewith. The present invention is, however, only concerned with castoroil compositions containing in addition to the acetic acid ester aglycol ether as solubilising agent in order to bring about or ensurecompatibility with the castor oil.

According to the present invention, therefore, a liquid for transmissionof power consists of castor oil, a glycol ether and an acetic acid esterof a polyhydric alcohol containingv before esterification not more thanthree hydroxyl groups in the molecule.

The following specific examples of brake fluids are typical embodimentsof the present .invention, but while I have described my invention asapplicable to fluid brake systems, it is to be understood that myinvention includes liquids equally applicable to fiuid powertransmission means 45 other than those used in brakes. The proportionsgiven are by volume. 7

Example 1 Percent 50 Castor oil 50 Diethylene glycol mono butyl ether 25Triacetin 25 The amount of glycol ether must be sufiicient to render thetriacetin compatible with the castor t oil. For this purpose, theminimum quantity necessary to retain the castor oil in solution is ofthe amount of triacetin, but equal quan- I titles of diethylene glycolmono butyl ether and triacetin have been found to give the best resultsfor the purpose of brake fluids.

The composition may be prepared simply by mixing the ingredients, butpreferably the glycol ether and the triaoetin are first mixed and thenadded to the castor oil. The triacetin may be prepared by any of thewell known methods, for example, by heating glycerol with glacial aceticacid and potassium disulphate to form diacetin which is separated andtreated with acetic anhydride.

A composition constituted as above will not gas in service until itreaches a temperature in the neighborhood of 190 C.

Example 2 Percent Castor oil 50 Diethylene glycol mono butyl ether 25Diacetin 25 This composition is prepared exactly as in Example 1, andthe properties are very similar.

Example 3 Percent Castor oil 60 Ethylene glycol diacetate 30 Diethyleneglycol mono butyl ether 10 The acetic acid esters of the glycols aremore easily compatible with castor oil than similar esters of glycerolbut in the proportions given above a solubilising agent is necessary inorder to avoid danger of separation of the castor oil from the glycolester.

Example 4 Percent Castor oil "a 50 Mono acetin 25 Diethylene glycol monobutyl ether 25 be carried out upon such of the compositions as,

are improved by this treatment. Blown or miscible oils are of highacidity and have no corresponding advantages.

Anticorrosion agents, coloring matter and special additions for thepurpose of obtaining exceptionally low freezing points or to form aprotective coating as a. residue when the brake fluid is evaporated byover-heating, may be added to the composition according to theinvention.

Compositions prepared according to the invention are found to have avery high vaporisation or gassing point, in some instances in theneighborhood of 200 C. and the fluids are without any detrimental actionupon the rubber or metal parts used in fluid brake systems.

Solubilisers other than the glycol ethers will bring about compatibilitybetween castor oil and acetic acid esters of polyhydric alcohols, butmay aflept seriously the valuable properties of the solution as a mediumin fluid transmission mechanism. While the invention has been describedmainly with reference to diethylene glycol mono butyl ether assolubilising agent, other glycol ethers may be employed in exactly thesame way as the mono butyl ether, in particular, the mono ethyl ether ofethylene glycol, and give liquids admirably suited for fluidtransmission purposes. Other high boiling point solvents for oils thanthe glycol ethers have not been found as suitable for the purpose ofsolubilising agents as the glycol ethers with the exception of diacetonealcohol which gives results comparable with the glycol ethers in mostinstances.

It will be appreciated that while compositions containing acetic acidesters of ethylene glycol and glycerol have been more particularlydescribed herein, esters of other diand tri-hydric alcohols may be usedsimilarly, in particular those of butylene and propylene glycol.Furthermore, mixtures of any of the acetic acid esters hereinbeiorementioned may be employed.

What I claim is:

l. A liquid for transmission of power consisting of castor oil, anacetic acid ester of a polyhydric alcohol containing. beforeesteriflcation not more than three hydroxyl groups in the molecule, anda glycol ether.

2. A liquid for transmission of power consisting of castor oil, anacetic acid esterof a polyhydric alcohol containing beforeesterification not more than three hydroxyl groups in the molecule, anda glycol butyl ether.

3. A liquid for transmission of power consisting of castor oil, anacetic acid ester of a polyhydric alcohol containing beforeesterification not more than three hydroxyl groups in the molecule, andan ether of ethylene glycol.

4. A liquid for transmission of power consisting oftriacetin, castor oiland a glycol butyl ether.

5. A liquid for transmission of power consisting of triacetin, 'castoroil and the mono ethyl ether of ethylene glycol.

6. A liquid for transmission of power consisting of ,ethylene glycoldi-acetate, castor oil, and ethylene glycol mono butyl ether.

'7. A liquid for transmission of power consisting of:

(a) Castor oil and triacetin wherein the proportion of castor oil is'approximately double that of the triacetin and (b) Sufiicient of aglycol ether to render the triacetin compatible with the castor oil.

BQA liquid for transmission of power consisting of the followingingredients in the proportion by volume stated:-

I Percent Castor oil 50 Triacetin 25 Diethylene glycol mono butyl ether25 WILLIAM PERCIV AL SMITH.

